This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. In the wake of various terrorist activities in the recent past, the development of a safer smallpox vaccine has come center stage. Large groups of the American population (infants, pregnant women, immunosuppressed individuals, and people with certain skin disorders) are not advised to receive the available Dryvax smallpox vaccine. This leaves a large number of people unprotected in the case of a biological terrorist attack. Towards the end of the smallpox eradication campaign, MVA (modified vaccinia Ankara) was being tested as a vaccine against smallpox for immunocompromised individuals. The vaccine was proven safe in humans;however, recent data suggest that MVA may be an insufficiently immunogenic vaccine to reliably elicit protective responses against variola or other highly pathogenic orthopoxviruses. Through this research we have discovered important aspects of the nature of how both replication-competent VV and replication-restrictive MVA interact with host dendritic cells (DCs), which could possibly lead to approaches to increase the protective capacity of MVA as a smallpox vaccine. The objective of the project has been to modify the currently available strain of MVA, so that novel vaccine variants can be derived which maintain safety and also have substantially enhanced abilites to elicit a long-lasting, high level cellular and humoral immune response that are cross-reactive with major virulent orthopoxviruses.